(1) Field of the Invention
The present invention generally relates to radiotherapy equipment and, more particularly, to a method and system for breast tissue immobilization for breast imaging and therapy.
(2) Description of Prior Art
Breast cancer is the most prevalent malignancy among women. Close to 211,000 cases of breast cancer were diagnosed in the United States in 2006 (Cancer Facts & Figures, 2006, American Cancer Society). The lifetime risk of any particular woman in North America getting breast cancer is about 1 in 7.
On a more promising note, breast cancer awareness and screening have resulted in the majority of breast cancers being diagnosed in the early-stage of the disease. The current standard of treatment for most early stage breast cancers is breast conservation therapy (BCT), consisting of lumpectomy followed by 6-8 weeks of radiation therapy, mostly irradiating the whole breast. Although the outcome of BCT is very favorable, the invasive surgical procedure and the lengthy radiation treatment significantly worsen the quality of life for such a large population of patients.
After years of clinical trial and studies, there are convincing arguments that the benefit of standard treatment of irradiating the breast following the lumpectomy is the sterilization effects of radiation on the micro extension of the tumor around the surgical bed (Morrow et al., J Natl Cancer Inst, 1995; 87:1669-73). This is the main hypothesis of the current push of accelerated partial breast irradiation (APBI). Instead of irradiating the entire breast, radiation is delivered to a segment around the lumpectomy cavity. With increased daily dose, the radiation treatment time is reduced from seven or eight weeks to four or five days, which could potentially impact the lives of thousands of cancer patients in a positive way.
Currently there are five Phase III clinical trials comparing APBI with whole breast irradiation. In the US, NSABP's B39 trial and RTOG's 0413 trial are ongoing (Arthur et al., J. of Clinical Oncology, 2005; 23:1726-35). This trial alone is targeted to enroll 3000 patients. Some early institutional study results are emerging, with 5 year reoccurrence rate ranging from 1-4% (Neihoff et al., Radiother Oncol 2006; 79:316-20; Chen et al., Cancer 2006; 106:991-9; Zannis et al., Am J Surg 2005; 190:530-8).
When irradiating breast, patient position is an emerging concern. Most radiation treatments are in supine position, while the most sensitive and specific MRI imaging are in prone position. Realizing the limitation of the supine position, a suggestion of treating patients with large breasts in a prone position was proposed by Merchant et al., (Int. J Radiat Oncol Biol Phys., 1994; 30:197-203). They found that, for large-breasted women treated in the prone position, the size of the high-dose region at the base of the breast was reduced. The tissue volume of normal lung and the heart included in the treatment fields was also decreased. Stepaniak et al., (Int. J. Rad Onc Biol Phys 2005; 63:S532-3) reported that analyses based on the 4D CT datasets from 3 patients showed that the average intra-treatment chest wall movement was less than 1 mm.
Another benefit of breast radiation treatment in the prone position is that it can reduce the motion resulting from cardiac systole and respiratory movement.
As concluded, prone position breast irradiation appears to be a simple and effective alternative to irradiation of the breast in the conventional supine position when the supine position is likely to result in unacceptable dose in homogeneity or significant doses to normal tissues.
When only irradiating the surgical bed locally, it is very important to treat the breast with precise geometric accuracy. Modern imaging technologies such as Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and Positron Emission Tomography (PET), can assist tumor localization with high geometrical accuracy. However, due to the pliable nature of breast tissue, it is a challenge to maintain the geometry unchanged during the entire process of imaging, treatment planning, and multi-fractional treatment delivery.
A number of breast tissue immobilization devices have been developed in the past. The most widely used procedure is that used in mammogram which uses two parallel plates to compress the breast tissue. Other methods were developed to meet different purposes, such as a compression-based device (Kaiser et al., J Magn Reson Imaging 1995; 5:525-8; Meyer et al., Radiology 1988; 169:266; Mark G. Fontenot, U.S. Pat. No. 6,589,254 Jul. 8, 2003; Bulkes et al., US publication 20050228267 Oct. 13, 2005), thermoplastic mask (Kaiser et al., J Magn Reson Imaging 1995; 5:525-8; Zeggelink et al., Medical Physics 2002; 29:2062-69), and contour cushions (Frederick N. Mellinger, U.S. Pat. No. 3,934,593 Jan. 27, 1976).
In U.S. Pat. No. 6,146,377, Lee et al. designed a breast-shaped device for biopsy and other invasive medical procedures. This device has a two-member structure to facilitate suction-induced breast stabilization/immobilization and has multiple openings to perform medical procedures in nipple/areola complex and other part of the breast.
Rioux et al. in US publication 2004/0215101 disclosed a two-layer device which has a medical device holder, open section for medical procedures, and vacuum/suction enabled breast immobilization mechanism. However, these existing methods and devices lack key features for effective APBI treatment: (a) immobilization must be precise, reliable, repeatable, and predictable; (b) applicable for prone position; (c) includes a mechanism to interlock the immobilizing device with the imaging couch or treatment bed; (d) be capable of reproducing the geometry when recurring procedure is needed; (e) have a stereotactic imaging registration mechanism for precise treatment setup; and (f) depress the untreated breast to minimize unnecessary radiation exposure. It is, therefore, an objective of current invention to address these needs.